الملخص

Abstract The study aims to determine the optimum thickness for some moderators which are used for obtaining thermal neutrons and for wide range of neutron energy (0.03 – 15 × 106) eV. The study involves two groups of materials: the first group consisted of H2O, D2O, Be, & C), while the second one are made of hydrocarbon materials (C25H52, C6H10O5, C6H12O6, C28H48O2, C18H34O2, C5H10O2, & Tissue equivalent material). The results revealed that the best moderator in the first group was water as it has a large scattering macroscopic cross section ∑)s), absorption macroscopic cross section (∑a) and it contains a high percentage of Hydrogen and that the lowest moderator within the same group is Graphite (c) since it has a higher diffusion coefficient (D), and also has a higher diffusion length (L). In the second group, it was found the best moderator was (C25H52), and the lowest one is (C6H10O5), for the same reasons mentioned above. Besides, that a lot of physical parameters are calculated which are related to neutron diffusion in the second group materials, such as (∑a), (∑s), (D), (L), (H%), (ξ), and molecular weight (M) for the hydrocarbon compounds.